Thermal acoustofluidics: ultrasonic manipulation of nanoparticles with temperature gradient

Important results from the project

We discovered the novel thermoacoustic streaming when the light-induced temperature gradients are created in a standing wave field. The underlying physics is well understood. It turns out to be difficult to achieve nanoparticle manipulation via thermoacoustic streaming. We therefore suppressed streaming using two miscible fluids and performed nanoparticle focusing using the device with an ideal vibration mode excited by the piezo actuation from the side. This new actuation method leads to a significant enhancement in acoustic energy density and hence improves the throughput.

Expected long term effects

The results obtained in this project are fruitful. The fundamental discovery regarding thermoacoustic streaming shows the potential to enable rapid spatiotemporal modulation of local streaming fields through fast reconfigurable optical fields. The enhancement of acoustic energy density in the microchannels of acoustofluidic devices using side actuation leads to high device performance, i.e., achieving high throughput under low input power. The result demonstrates a clear potential for acoustophoresis devices to better meet clinical standards.

Approach and implementation

The plan for the first year was followed almost perfectly, that we discovered the novel thermoacoustic streaming and understood its underlying mechanisms. The original plan for the second year turned out to be very difficult to implement. Therefore, a backup plan was used for manipulating nanoparticles. The implementation of nanoparticle manipulation turns out to be successful using the backup plan. Besides, an unexpected result regarding the themoacoustic streaming induced by frictional heating was also obtained in the second year, which was not planned at the beginning.